There are various methods used to control pests on large domestic animals such as livestock. Commonly employed methods include sprays and dusts, back rubbers and dust bags, and ear tags or tapes.
Sprays, dusts, and pour-on applications of pesticide involve manually applying pesticide to the animal's back. Although this method can be effective, it requires additional herding and handling and is generally not practical for large ranches or for free-range cattle.
Back rubbers and dust bags are devices that are impregnated or filled with pesticide and suspended in a pasture in proximity to a salt lick, water supply or place the animals frequent. The animals make contact with these devices in the normal course of their routine. The dust bag or back rubber may also be located in a gateway which leads to a salt lick or water supply and which forces the animal to contact the device. Again, this method of insecticide application can be effective, but may not be practical for certain situations such as large ranches or free-range cattle.
Ear tags are widely used and are generally made of a molded polymer matrix impregnated (i.e., saturated or immersed) with a substance such as a pesticide or parasiticide. These ear tags or tapes are attached to animals by piercing the ear with a sharp post and corresponding locking receptacle or with adhesive. The pesticide slowly leaches from the carrier material and is deposited onto the animal. The animal then spreads the material by moving its head from side to side and by rubbing alongside other animals.
The delivery of substance from these known ear tags is problematic. Among other delivery problems, the tags release the substance after packaging such that it crystallizes on the surface of the tag itself, thereby exposing the user to a high concentration of the pesticide. Another significant problem is that the output of the tags is not constant. Initially, they supply excessive doses of the substance, but over time, their output falls below an effective or lethal level, where it remains. The tags then supply doses that are less than lethal for weeks or perhaps months before their nominal expiration date. Unfortunately, exposing parasites to a sub-lethal dose causes future generations of these pests to develop a resistance or immunity to the substance. In turn, for a given area in which the tags are used, the type of tags used must be frequently changed so that the pests are exposed to a new substance to which they have not developed a resistance. This can create excess inventory of tags that are no longer effective, and can undesirably result in tags that have only been worn by the animals a short time before having to be replaced. The labor and costs associated with “re-tagging” animals mid-season can be quite large.
Moreover, the types of substances which can be used to saturate known ear tags is generally limited due to solubility and/or compatibility between the saturating substance and the polymer matrix. For example, compounds like ivermectin and spinosad have relatively high molecular weights and poor solubility in polymers such as polyethylene. These compounds are essentially incompatible with conventional ear tags.
Another problem with known ear tags is the inherent limit in the amount of liquid pesticide that can be saturated into a given size polymer matrix. It is not practical to produce a device large enough to contain sufficient insecticide to kill pests for an entire season. The size of the device would be such that it interferes with the animal's normal routine and would likely cause discomfort or injury to the animal, such as eye irritation, drooping ears, tears in the ear at the location of attachment, etc.
It would be desirable to have an application method and dispenser that is capable of dosing a repeatable, prolonged, and lethal application of pesticide to an animal with no gradual decline, but rather, a sudden and complete cessation of exposure, and does not require further herding, handling or contact with the animal.